1. Field of the Invention
The present invention relates to an electromagnetic rotary driving device which is suitably adapted as a rotary driving device for an air flow rate control device of an exhaust gas control apparatus for an automobile.
2. Description of the Prior Art
In a conventional proportional solenoid, such as that used for various types of devices as shown in FIG. 1, a cylindrical coil 101 is arranged inside a cylindrical case 100. A core 102 is disposed at the center of the coil 101. A plunger 103 is arranged to define a predetermined air gap 104 between itself and the core 102, thereby constituting a movable section. An oil-impregnated plastic member 105 is arranged at the center of the core 102 and supports the plunger 103. The proportional solenoid has an air passage 106 and is used for controlling the flow rate of air.
In the device shown in FIG. 1, the plunger 103 can only have a stroke of about 5 mm. When the device is used, for example, in an exhaust gas control apparatus for an automobile or the like, the device is required to control the flow rate in the range of 0 to 600 l/min. For this purpose, the air passage 106 must have a diameter of 14 mm or more, resulting in a very large device. Furthermore, since the air gap 104 is opened or closed by the linear movement of the plunger 103, the device is subject to the problem of vibration.